Design and development of a helium injection system to improve external leakage detection during liquid nitrogen immersion tests
When He gas is injected from room temperature into boiling liquid N2, boiling is suppressed, leaving liquid surface flat like a mirror. Although the qualitative explanation for this phenomenon is known [Minkoff G J et al. Nature 1957;180(4599):14134.], it has not been studied quantitatively and comprehensively yet. In this report, we made careful simultaneous measurements of temperature and weight variation of the liquid. The results clearly indicate that the boiling suppression is caused by cooling of the liquid with “internal evaporation” of N2 into the He bubbles.